1. Field of the Invention
The present invention relates to a measuring apparatus and a plasma processing apparatus, and more particularly, to an apparatus for optically measuring an examination target.
2. Description of the Related Art
When etching or film formation is performed on, for example, a semiconductor wafer (hereinafter, referred to as a wafer), controlling of a temperature of the wafer is relevant to a film forming rate or an etching rate of the wafer, thereby affecting features of a film or a shape of a hole formed in the wafer. Therefore, it is important to improve accuracy of controlling the temperature of the wafer in order to improve processing accuracy of the wafer, yield, and productivity of the wafer.
Thus, a method of measuring a temperature of a wafer by using a fluorescent thermometer or a resistance thermometer for measuring a temperature of a rear surface of the wafer, or the like has been conventionally suggested. Patent Reference 1 discloses an apparatus for measuring a temperature of a wafer based on an interference state between measuring light and reference light, including a light source, a unit for dividing light emitted from the light source into the measuring light and the reference light, and a unit for reflecting the divided reference light and changing an optical path length of the reflected reference light, and a photodetector for detecting an interference state between the measuring light reflected by the wafer and the reference light, by irradiating the wafer with the measuring light.
On the other hand, by using a spectroscope using a charge coupled device (CCD) array or a photodiode array as a detector, spectrum data may be acquired instantly by photodetection elements arranged in an array shape. Since the spectrum data represent characteristics of light incident to the spectroscope, the temperature of the wafer may be measured by using the spectrum data.
However, in the spectroscope using a CCD array or a photodiode array, a wavelength resolution power or the sampling number in wavelength domain is determined according to the number of elements, and thus it is physically impossible to increase the wavelength resolution power to be higher than the number of elements. In addition, the wavelength resolution power is limited to 3648 in a visible region and to 512 to 1024 in an infrared region, and thus the wavelength resolution power cannot be increased more than the above limitations. Thus, spectrum of a high resolution cannot be implemented when using, in particular, infrared rays, compared with visible rays.
On the other hand, there is a correlation between the wavelength resolution power and a thickness of an examination target that can be measured, and the lower the wavelength resolution power becomes, the more the thickness of the measurable examination target is limited. Therefore, up to now, a thickness of the examination target that can be measured by using a general CCD array or a photodiode array is limited to be very thin. For example, in a plasma processing apparatus, a thickness of a wafer may be measured; however, a thick member having a thickness to a certain degree, such as a focus ring, or the like cannot be measured.
3. Prior Art Reference
(Patent Reference 1) Japanese Laid-open Patent Publication No. 2010-199526